1. Field of the Invention
The present invention concerns screws, nuts and bolts made of a composite material comprising a ceramic matrix reinforced with refractory fibers, and more specifically, assembling members or fasteners comprising firstly a threaded rod possibly including a head, and secondly at least one nut cooperating with the rod, the members being made of a ceramic material obtained by sintering, under the load of a refractory powder, and incorporating reinforcement filaments in the form of trichite or "whiskers".
2. Background Information
The construction of the invention more particularly, although not exclusively, uses composite materials with a ceramic matrix constituted by SiAlON or Si.sub.3 N.sub.4, and reinforced with silicon carbide and/or silicon nitride trichites. These materials are respectively described in the French patent No 2.586.246 and 2,610.921.
The reinforced ceramic materials have the following advantageous characteristics:
almost isotropic reinforcement, PA1 natural resistance to oxidation, PA1 ability to be used at temperatures that reach or exceed 1200.degree. C., PA1 good thermomechanical properties, PA1 good tenacity and good resistance to thermal shocks, PA1 good machinability as compared with other ceramic materials.
Because of their specific properties, especially the hardness and resistance to thermal and mechanical shocks, these materials are mainly used in hot tribology and are rarely exploited for structural uses owing to their elastic characteristics, wherein the materials are considerably rigid and fragile.
Recently, there has been considerable interest in constructing structures that can be assembled and dissembled and are also able to resist high temperatures reaching or even exceeding 1200.degree. C.
With this aim in mind, it is out of the question to consider making use of metallic screws, nuts and bolts, because they are unable to withstand such high temperatures. However, the ceramic composite materials, of the type described above, have properties and special characteristics that make the simple reproduction of metallic screws, nuts and bolts into reinforced ceramic screws, nuts and bolts for use in assembling structures subjected to high mechanical traction, bending and shearing stresses unsatisfactory. Added to this is the difficulty of machining and the fragility of the reinforced ceramic materials, especially as regards tensile strength. This makes it impossible to obtain acceptable resistance to rupture in light of the mechanical stress that the screws, nuts and bolts will confront.